Microsoft Windows Worm Abuses Weak Password Practices

A new worm targeting Microsoft Windows is squiggling its way around computer networks courtesy of weak passwords.

Dubbed Morto, the worm doesn’t use a vulnerability, but instead propagates by compromising Remote Desktop connections on a network through brute forcing attacks. So far, the overall number of detections is relatively low - researchers at F-Secure put the number in the thousands – but reports of increased traffic on port 3389 prompted Microsoft to issue an advisory about the worm Aug. 28.

“Once a new system is compromised, it connects to a remote server in order to download additional information and update its components,” blogged Hil Gradascevic, a researcher with Microsoft’s Malware Protection Center. “It also terminates processes for locally running security applications in order to ensure its activity continues uninterrupted. Affected users should note that a reboot may be required in order to complete the cleaning process.”

While 74 percent of the computers known to be affected are running Windows XP, infections have also been found on Windows Vista, Windows 7 and Windows Server 2003 and 2008.

In a separate blog post, Microsoft’s Holly Stewart and Matt McCormack noted Morto attempts to compromise more than just the 'Administrator' account when brute forcing RDP connections with a dictionary attack. It also tests the affected machine's Internet connectivity by attempting to connect to IP 74.125.71.104, an IP owned by a legitimate corporation and believed to be unrelated to malware. If unsuccessful, it then cycles through IP addresses on the affected computer's subnet and attempts to connect to targeted hosts using various usernames such as “admin” or “backup.”

Mikko Hypponen, chief research officer at F-Secure, told SecurityWeek that companies looking to protect themselves should make sure their RDP servers are not exposed to public networks by accident. The next step is to ensure strong passwords are being used that can’t be cracked by a wordlist or reasonable brute force attack, he added.

Marc Maiffret, CTO of eEye, described the worm as reminiscent of older worms such as Slammer and CodeRed, and contended that if “there are companies in this day and age being compromised by Morto, we have bigger problems to worry about than the “APT” or Stuxnet.”

“You should never allow RDP access directly from the Internet, without, at the very least, requiring VPN authentication, before gaining access to corporate servers remotely,” he advised.